1. Field of the Invention
The present invention relates to radiation detecting apparatus used in X-ray photographing systems and others. In the present specification, description will be given on the presumption that the term xe2x80x9cradiationxe2x80x9d includes not only electromagnetic waves such as X-rays, xcex3-rays, and the like, but also xcex1-rays and xcex2-rays.
2. Related Background Art
FIG. 14 shows an example of a sectional view of a pixel in a conventional X-ray sensor (radiation detecting apparatus). FIG. 15 shows an example of a schematic circuit diagram of an X-ray sensor and FIG. 16 an example of an X-ray photographing system.
In the X-ray sensor shown in FIG. 14, a pixel is composed of an amorphous silicon photodiode 43 and a thin film transistor (TFT) 44. A phosphor layer 41 is placed above an X-ray incident surface, i.e., an upper surface of the photodiode 43 to convert X-rays to visible light. As shown in FIG. 15, pixels are arranged in a two-dimensional pattern and driven by matrix drive. Namely, the pixels are driven by a gate driver 22 connected to common gate lines and data is read out by a read circuit 21 connected to common data lines. The X-ray sensor in this illustration is comprised of the phosphor layer, amorphous silicon photodiodes, and TFTs, but some sensors can be comprised of the phosphor layer and CCDs. As shown in FIG. 16, X-rays carrying object information, having passed through an object 30, are read by the X-ray sensor 35.
Normally, X-rays having passed through an object consist of X-rays carrying effective object information, and scattered X-rays. It is generally known that the scattered X-rays due to the Compton effect or the like have low energy and cause degradation of image quality.
The reason for it is that the phosphor emits light when receiving the scattered X-rays of low energy from the object and information carried thereby is also read to cause the degradation of image quality.
In some X-ray photographing systems using the conventional X-ray sensor, a grid 34 for removal of scattered X-rays as shown in FIG. 16 is provided for reducing influence of the aforementioned scattered X-rays. In this structure, however, the grid appeared in images to degrade the quality of image in certain cases.
Namely, in order to achieve much higher image quality, it was necessary to solve the problems including the problem of degradation of image quality due to the scattered X-rays, the problem of appearance of the scattered X-ray removing grid in images, and so on.
An object of the present invention is therefore to provide radiation detecting apparatus capable of reducing the scattered X-rays to prevent the degradation of image quality and preventing increase in the radiation incident to an object.
In order to achieve the above object, the present invention provides a radiation detecting apparatus adapted to let a radiation into a semiconductor layer and read a charge generated thereby, wherein a depleted region in a semiconductor layer, which is depleted with application of an electric field, is controlled by a variable voltage source.
In another aspect X-rays having passed through an object are made incident into the apparatus from a side of a non-depleted region in the semiconductor layer. Further, the non-depleted region has a function of absorbing scattered X-rays of low energy.